linux-kernel - [RFC PATCH v1 3/3] sched: loadbalancer hacks for forced packing of tasks

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Date:	Mon, 27 Apr 2009 02:17:07 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arjan van de Ven <arjan@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vatsa <vatsa@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	Gregory Haskins <gregory.haskins@...il.com>,
	Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arun Bharadwaj <arun@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: [RFC PATCH v1 3/3] sched: loadbalancer hacks for forced packing of
	tasks

Pack more tasks in a group so as to reduce number of CPUs
used to run the work in the system.

Just for load balancing purpose, assume the group capacity
has been increased by group_capacity_bump_pct()

Hacks:

o Make non-idle cpus also perform powersave balance so
  that we can pull more tasks into the group
o Increase group capacity for calculation
o Increase load-balancing threshold so that even if a
  group is loaded by group_capacity_bump_pct, consider
  it balanced

*** RFC patch for discussion ***

Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
---

 kernel/sched.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index f88ed04..b20dbcb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3234,6 +3234,7 @@ struct sd_lb_stats {
 	int group_imb; /* Is there imbalance in this sd */
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
 	int power_savings_balance; /* Is powersave balance needed for this sd */
+	unsigned int group_capacity_bump; /* % increase in group capacity */
 	struct sched_group *group_min; /* Least loaded group in sd */
 	struct sched_group *group_leader; /* Group which relieves group_min */
 	unsigned long min_load_per_task; /* load_per_task in group_min */
@@ -3321,12 +3322,16 @@ static inline void init_sd_power_savings_stats(struct sched_domain *sd,
 	 * Busy processors will not participate in power savings
 	 * balance.
 	 */
-	if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+	if ((idle == CPU_NOT_IDLE &&
+		sched_mc_power_savings <
+		POWERSAVINGS_INCREASE_GROUP_CAPACITY_1) ||
+		!(sd->flags & SD_POWERSAVINGS_BALANCE))
 		sds->power_savings_balance = 0;
 	else {
 		sds->power_savings_balance = 1;
 		sds->min_nr_running = ULONG_MAX;
 		sds->leader_nr_running = 0;
+		sds->group_capacity_bump = group_capacity_bump_pct(sd);
 	}
 }
 
@@ -3586,6 +3591,9 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 
 		if (local_group && balance && !(*balance))
 			return;
+		/* Bump up group capacity for forced packing of tasks */
+		sgs.group_capacity = sgs.group_capacity *
+				sds->group_capacity_bump / 100;
 
 		sds->total_load += sgs.group_load;
 		sds->total_pwr += group->__cpu_power;
@@ -3786,6 +3794,10 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 	if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load)
 		goto out_balanced;
 
+	/* Push the upper limits for overload */
+	if (100 * sds.max_load <= sds.group_capacity_bump * SCHED_LOAD_SCALE)
+		goto out_balanced;
+
 	sds.busiest_load_per_task /= sds.busiest_nr_running;
 	if (sds.group_imb)
 		sds.busiest_load_per_task =

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